We propose to study the electronic and molecular structure of active centers in metalloproteins using primarily magnetic resonance and Mossbauer spectroscopy. Our main interest focuses on iron proteins that interact with the O2-H2O-H2O2 redox system. The ultimate goal is to elucidate structural and dynamic features that control the reaction pathways. Research will proceed along several lines. (i) We will investigate the events leading to dioxygen activation in cytochrome P450CAM, with specific emphasis on complex formation between the monooxygenase and the 2Fe-2S rdox/effector protein, putidaredoxin. Comparisons of EPR/ENDOR parameters of the isolated proteins with those of the bimolecular complex should reveal effects of spin-spin interactions and/or conformational changes. To support assignments, the homology of putidaredoxin with the known structure of algal ferredoxin will be examined by ENDOR in H2O/D2O. (ii) Attempts will be made to trap an electron, by low temperature radiolysis, on the heme-O2 complex of substrate-bound oxyP450CAM. EPR and ENDOR will be used to probe for the expected heme-O2 radical and its reaction products on annealing. (iii) To follow up on the observation of an EPR signal in deoxymyoglobin (21) we will explore other S=2 states in heme and non-heme iron proteins for such signals. The energy levels and transition probabilities will be modeled by a spin Hamiltonian with a distribution of parameters. Single-crystal and high-frequency EPR, as well as Mossbauer spectroscopy, will be used to gain further insight into the distribution of energy levels in these systems. (iv) In collaboration with chemists locally and at other universities we will continue our EPR and Mossbauser studies of higher oxidation state intermediates in the peroxidases and catalases and of the spin-coupled binuclear clusters in hemerythrin and purple acid phosphatase. Model systems will be analyzed for comparison with metalloproteins if they promise further insights.